The present invention relates to magnetic recording heads, and more particularly, to heads that are used in video tape recording such as for electronic news gathering apparatus.
In small portable recorders it is customary, due to the size and weight limitations, to record a video signal using two channels, one for the luminance signal and the other for the chrominance signal. The chrominance signal is usually directly recorded at base band, while the luminance signal is usually recorded using frequency modulation of a high frequency carrier. This approach allows a smaller headwheel to be used, while permitting the bandwidth and the signal-to-noise ratio to remain within acceptable limits. However, this approach does have problems. In particular, because of slight variations in tape tension across the width of the tape, one side of the tape may stretch slightly more than the other side during either recording or playback. This results in the chrominance signal begin slightly time displaced with respect to the luminance signal, and is therefore called "interchannel time displacement". To avoid this problem, it is desired to have the two recording tracks as close together on the tape as possible. Further, in order to minimize the size of the cassette, the length of the tape should be made as short as possible. This also requires that the recorded tracks should be made as close as possible. However, there is another problem in recording; during playback a head can pickup the recorded signal from an adjacent track, and during both record and playback inductive coupling between heads can occur. These effects are called "crosstalk". The crosstalk in the first case is proportional to the recorded wavelength, while the second crosstalk, since it is an inductive effect, increases at higher frequencies for a given fixed distance between adjacent heads. Therefore to minimize crosstalk, the heads should be located as far apart as possible. This clearly is in conflict with the requirement for minimizing the interchannel time displacement and tape length. It is possible to have the recording heads set at an azimuth angle to reduce the crosstalk, but this does not solve the problem since mistracking can occur which causes crosstalk despite the head angle.
It is therefore desirable to have a magnetic recording and playback head structure which minimizes both sources of crosstalk and interchannel time displacement.